This is documentation for Mathematica 6, which was
based on an earlier version of the Wolfram Language.
 Built-in Mathematica Symbol

# TraceScan

 TraceScan[f, expr]applies f to all expressions used in the evaluation of expr. TraceScan[f, expr, form]includes only those expressions which match form. TraceScan[f, expr, s]includes all evaluations which use transformation rules associated with the symbol s. TraceScan[f, expr, form, fp]applies f before evaluation and fp after evaluation to expressions used in the evaluation of expr.
• All expressions are wrapped in HoldForm to prevent evaluation before f or fp are applied to them.
• The function fp is given as arguments both the form before evaluation and the form after evaluation.
• TraceScan[f, expr] returns the result of evaluating expr.
Print all expressions used for evaluation:

Count additions and multiplications of machine numbers needed for a numerical computation:
 Out[1]=

A recursive definition for finding Fibonacci numbers:
Count calls to fib required:
 Out[2]=
Redefine fib so that it saves results:
Count calls to fib required:
 Out[4]=
The second time through it takes only one call since the value was saved:
 Out[5]=
New in 2